MIT astronomers want light and radiation from X-rays of a nearby black hole – systems that have a star around them, and are sometimes eaten by a black hole. They analyze the echoes from such systems in order to recreate a nearby, extremely dangerous area of black hole.In a study published today in the Astrophysical Journal, researchers reported using a new automatic search tool, which they compiled into a “Recovery Machine,” to compile satellite data to detect signs of black hole echoes. In their search, they found eight new binaries echoing through black holes in our galaxy. Previously, only two such systems in the Milky Way were known for extracting X-ray echoes.
In comparing echos across all systems, the team included a general picture of how a black hole appears during an eruption. In all systems, they have observed that the black hole begins to have a “hard” shape, releasing a corona of high-powered photons and a jet of parallel particles introduced at close range at light speeds. The researchers found that at some point, the black hole emits a single, high-intensity light, before moving to a “soft,” state of low energy.
This last flash may be a sign that the corona of the black hole, the plasma area with great potential just outside the black hole border, expands briefly, releasing the last burst of strong particles before disappearing completely. “The role of black holes in the evolution of the galaxy is a prominent question in modern astrophysics,” said Erin Kara, an assistant professor of physics at MIT. “Interestingly, these black holes appear to be ‘small’ black holes, so by understanding the explosion in these nearby small systems, we can understand how the same explosion in the large black holes affects the galaxies in which they live.”The first author of the study was MIT graduate student Jingyi Wang; Other co-authors include Matteo Lucchini and Ron Remillard at MIT, as well as participants from Caltech and other institutions.
X-ray echoes to create map near black hole
Kara and her colleagues use X-ray echoes to create a map of the area near the black hole, in the same way that bats use sound eclipses to navigate the surrounding area. When a bat makes a call, the sound can jump off the block and return to the bat as an echo. The time it takes for the echo to reconnect is the distance between the bat and the obstacle, which gives the animal a mental map of the surrounding area.In the same way, the MIT team is looking to make a map of the area near the black hole using X-ray echoes.
The echoes represent a time delay between two types of X-ray light: direct light from the corona, and light from the corona emanating from a gas-expanding disk and respiratory dust.The time when the telescope receives light from the corona, compared with when it receives X-ray echoes, provides a measure of the distance between the corona and the accretion disk. Observing how this delay changes can reveal how the corona of the black hole and disk appear as the black hole eats away at star objects.
Echo evolution
In its new study, the team developed a search algorithm to compile data captured by NASA star Neutron Interior Composition Explorer, or NICER, a high-resolution X-ray telescope located at the International Space Station. The algorithm selected X-ray binary systems of 26 black holes that were previously known to emit X-ray explosions. Of the 26, the team found that 10 systems were close enough and bright enough that they could detect X-ray reactions during an explosion. Eight out of 10 were previously unknown to respond.
“We are seeing new duplicate signatures in eight sources,” Wang said. “Black holes vary in frequency five to 15 times the size of the sun, and they are all in binary systems with normal, low-mass, sun-like stars.”As a separate project, Kara is collaborating with MIT academics and music academics, Kyle Keane and Ian Condry, to convert X-ray echo output into audible sound waves.The researchers then applied the algorithm to 10 black hole banners and divided the data into groups with similar “spectral time” features, i.e., the same delays between high-resolution X-rays and echoes re-analyzed. This helped to quickly track changes in X-ray echoes at all stages during the black hole explosion.
The team identified the same change across systems. In the first “severe” case, when the corona and jet of high-energy particles dominate the dark hole, they found a curvature that was shorter and faster, in a series of milliseconds. This difficult situation lasts for several weeks.During this difficult transition period, the team found that shortness of time increased temporarily across all 10 systems, meaning that the distance between the corona and the disc also increased significantly. One explanation is that the corona may expand inward and outward, in the final high-energy explosion before the black hole completes its delicious and quiet meal.
“We are just beginning to be able to use these light signals to rebuild areas near the black hole,” Kara said. “We have now shown that these echoes are often seen, and we are able to explore the connection between the black hole disk, plane, and corona in a new way.” The study was supported, in part, by NASA.
Spread across our Milky Way galaxy tens of millions of black holes – super-gravitational springs of space, in which emissions, even light, can never escape. The black holes are black by definition, except for the occasional feeding. As the black hole absorbs gas and dust in the surrounding star, it can emit a spectacular X-ray light that bounces and responds to the gas breathing, briefly illuminating the surrounding black hole.
Source Journal Reference: Jingyi Wang, Erin Kara, Matteo Lucchini, Adam Ingram, Michiel van der Klis, Guglielmo Mastroserio, Javier A. García, Thomas Dauser, Riley Connors, Andrew C. Fabian, James F. Steiner, Ron A. Remillard, Edward M. Cackett, Phil Uttley, Diego Altamirano. The NICER “Reverberation Machine”: A Systematic Study of Time Lags in Black Hole X-Ray Binaries. The Astrophysical Journal, 2022; 930 (1): 18 DOI: 10.3847/1538-4357/ac6262
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